Lore

Future Press game guide description: "Iosefka is an earnest, kindhearted doctor of the Healing Church who oversees the clinic in Central Yharnam. She cares deeply for her patients' well-being and strictly forbids you from re-entry into the facility for fear of exposing them to the scourge, but is still willing to provide you with her valuable experimental blood vials."

Iosefka is a doctor for the Healing Church who oversees the clinic known as ‘Iosefka’s Clinic’ in Central Yharnam. After the player leaves the room they wake up in and reload the area, Iosefka will close and lock the door behind them, seemingly as if she was waiting for them to leave.

The Clinic Iosefka operates is where foreigners to Yharnam and patients come to receive Blood Ministration. Yharnam is the home of blood ministration. The Healing Church controls all knowledge on blood ministration, and all varieties of blood. Once a patient has had their blood ministered, a unique but common treatment in Yharnam, successive infusions recall the first, and are all the more invigorating for it. Blood ministration is the pursuit of communion, and involves the transfusion of unknown blood. Visitors to Yharnam often come to the city to receive this blood as a means of treating whatever form of sickness they have. Before receiving the transfusion, patients must sign a contract with their Blood Minister, though what is included in this contract is never explicitly revealed.

From this information it is clear that Iosefka is affiliated with the Healing Church and her role is to provide visitors to Yharnam with blood that will heal them. But there is certainly more to her than that. Iosefka is a special Church doctor, and therefore a specialist in experimentally backed blood ministration and the scourge of the beast. She is well aware that the blood she is giving to her patients will have some seriously adverse side-effects, and this is a possible reason as to why she will not allow you back into her clinic after your blood has been administered to. She will tell you “the patients here in my clinic must not be exposed to infection” though as a specialist of blood she must already know that it is the blood that causes the infection. Iosefka knows that the hunt drives hunters mad for blood, turning them into beasts, and she therefore does not want to risk her research being brought to an end by some bloodthirsty hunter. If you attack her door she will eventually say: “You are no more than a beast. I should’ve known…” indicating she knows what happens to hunters. She is seemingly sympathetic to the player’s cause though, and will give them vials of precious blood.

So what is her true agenda? Iosefka is seeking a cure for the scourge, just like any good doctor would. Her method involves a slow and careful blood refinement process, which was likely devised by Iosefka herself. We are not told what Iosefka hopes to achieve from refining the blood, but there are some likely conclusions to draw. Iosefka knows much about blood, and what she hopes to refine from the blood is the blood borne infection that causes those blood is ministered to, to succumb to the Scourge of the Beast. When we look at Iosefka’s blood vial we can see that it is not red but rather an amber, light yellow color, and yet it is called blood and its affects are even better than regular blood vials. Iosefka’s vials are “highly invigorating” and restore a larger amount of HP. Evidently Iosefka is on to something. Because of the coloration of the blood we can make an educated guess that she is refining it of the red blood cells leaving just the plasma. This quote from The Paleblood Hunt (https://docs.google.com/document/d/1JL5acskAT_2t062HILImBkV8eXAwaqOj611mSjK-vZ8/edit) by Reddit user Redgrave explains the significance of this succinctly:

“I am not a doctor, nor will I pretend to be. As such I am likely vastly oversimplifying things, so take my explanation with a grain of salt. Blood consists of three distinct ingredients. First are Erythrocytes, typically referred to as Red Blood Cells. Red blood cells travel through the body of a human being and distribute oxygen to the body's tissues. Red blood cells are the primary means of life support and nutrition for the body's tissues. Second is Plasma. Approximately half of blood is plasma, a liquid that serves as means of transportation for the blood cells which carry out their task in supporting the human body. When blood is centrifuged to separate the ingredients, we find something very interesting about plasma. Plasma that has been separated from clotting proteins and blood cells is actually an amber, light yellow color. This liquid is referred to as Serum, or sometimes pure blood as it is the liquid blood in itself without any other ingredients. The third ingredient of blood are the Leukocytes, or White Blood Cells. White blood cells exist as part of the human body's immune system; they attack infectious invaders, foreign substances, and clean after old and dead cell structures.

Blood is such a central theme in Bloodborne, everything revolves around Blood, even the title. Especially the title. Bloodborne. A bloodborne pathogen, a disease of the blood, this is what the Scourge of the Beast is. It's an infection, a disease that spreads from person to person through the transfusion of blood. Master Willem sternly reminds Laurence that: "We are born of the blood. Made men by the blood. Undone by the blood." The scourge infects the victim by attacking and tainting their blood, corrupting them.

Now look at the Kin, ascended mortals who have become Kin of the Cosmos. They have escaped the taint of the Scourge, moving past it. Indeed they bleed a clear, amber liquid; serum, to be exact. The Kin of the Cosmos have cleansed their blood of the tainted scourge, separating it from the other ingredients and becoming pure beings.”

Redgrave extrapolates that the blood that is a clear a amber, light yellow color is the blood of the Kin of the Cosmos. Whether Iosefka obtained this blood through contact with the Choir or Ebrietas or whether standard Yharnam blood that has been carefully refined actually is kin blood, is unclear. But Iosefka appears to be coming close to a vital breakthrough. If her work was allowed to continue it may have led to the ending of the Scourge of the Beast, as the blood she could treat the patients with would actually be kin blood, which is cleansed of the beastly taint. Unfortunately, Iosefka is removed from the game early on in the night and replaced by an imposter. Entering the clinic from the back entrance, the player finds a Celestial Emissary standing where Iosefka used to stand. When the player kills this emissary it will drop one of Iosefka’s Vials, bringing to a close a shining light, in the dark of the hunt…

Theories

Iosefka was already creating Celestial Emissaries before the Imposter took over

Though commonly held in high regard, there are a number of interesting facets to Iosefka that darken her untarnished image. After the Imposter takes up residence at the clinic, she will start creating Celestial Emissaries using kin blood. If Iosefka was creating kin blood in her clinic (see the lore section) then that might explain where the Imposter got her hands on it, if she hadn’t already brought it with her. We see out the back of Iosefka’s clinic that there are a number of graves, and a secret entrance that leads to the Forbidden Woods, through a cave of mysterious liquid that could easily dissolve a body (as we see in the Research Hall of the Healing Church). It is very unlikely that the Imposter placed the ladder down to the Forbidden Woods there, as it is an incredibly long descent. Perhaps it is just the nature of the blood ministration that patients end up dying, but the presence of a locked graveyard implies Iosefka had something to hide, and besides, isn’t blood ministration supposed to heal patients? So why would Iosefka need to bury bodies in her backyard behind lock and key or dump them in a pool that will remove any traces of evidence? When we enter the clinic from the Forbidden Woods, we assume that the Celestial Emissaries we see were created by the Imposter, indeed one of them drops Iosefka’s Vial and is standing right where she used to stand, indicating that this is Iosefka’s eventual fate. But what if that work began before the arrival of the Imposter?

Each Emissary that is created by the Imposter seems to be alive, and often is in some way mimicking the behaviour of the person it used to be before the transformation. But there is one Celestial Emissary we find, right in the back room of the clinic. Not in a place where the Imposter works, but rather in a room that seems to be almost secretive in nature. On the gurney in this room we find a deceased Celestial Emissary, and looking closely at its right hand and thigh we can see that this Emissary was once human, though the transformation wasn’t completed, almost as if the process was being developed. Where did this Celestial Emissary come from? The body count doesn’t seem to match up with the number of patients sent to the clinic, almost as if the patient was there prior to the Imposter arriving. Perhaps then, fear of exposure is the true reason Iosefka did not want the player to come back into the clinic.

The opening cinematic of the game reveals that the player has received a blood transfusion from one of the blood ministers of Yharnam (a title the character is credited with in Bloodborne's credits) and this character mysteriously vanishes after the cinematic. In the back rooms of the clinic we find the body of a celestial emissary that has mostly transformed from its original human state, revealing a hand and thigh that still have human skin. We also find an empty wheelchair in the clinic's hallways. This emissary is present from the very beginnings of the game, even before the imposter arrives on the scene, as revealed by a glitch and does not match the body count of the refuges the player is able to send to the clinic. It should also be noted that all of the celestials Imposter Iosefka creates are survive the process. It is certainly possible that the emissary was another of the other patients in the clinic, but considering the evidence gathered, it may be that that celestial emissary is the remains of the blood minister from the opening cinematic.

Dialogue

Upon speaking with her for the first time:
"Are you… out on the hunt? Then I'm very sorry, but… I cannot open this door. I am Iosefka.
The patients here in my clinic must not be exposed to infection.
I know that you hunt for us, for our town, but I'm sorry. Please.
This is all that I can do.
(Gives Iosefka's Blood Vial' x1)
Now, go. And good hunting."

Upon speaking with her when in possession of Iosefka's Blood Vial:
"Are you still in need of something? But I have nothing more to offer.
Please, try to understand my position. I can only pray, for a fruitful hunt."

Upon speaking with Iosefka when you are not in possession of Iosefka's Blood Vial:
"You are safe, thank goodness. But I’m afraid nothing will change.
I cannot open the door. I’ll do what I can, of course.
Perhaps this will help you, if only in some small way.
(Gives Iosefka's Blood Vial' x1).
Now, go. I pray for your safety."

Upon receiving your fourth Iosefka's Blood Vial:
"Ah, you are safe. Thank goodness. But I'm afraid nothing will change my mind.
I cannot open the door. I'll do what I can, of course.
Perhaps this will help you, if only in some small way.
(Gives Iosefka's Blood Vial' x1)
This night is long, but morning always comes. Someone of your caliber won’t fail us, I am certain.
And once the night of the hunt ends, we can speak face-to-face.
Then I can finally see what you look like.
I shouldn’t be thinking this but I am rather looking forward to it.
So please, be careful out there."

Upon speaking with Iosefka after receiving your fourth Iosefka's Blood Vial, but you are still in possession of one:
"I'm sorry…I have nothing else to offer you. I will pray for your safety.
May light shine upon this night, and your fortunes."

If you attack the door while Iosefka is still there:
"Ahh! Ohh!

After attacking the door again:
"Please stop! It's beasts you hunt. Why are you behaving like one?
This can't be the real you. Please, stop…."

Talking to her again, but this time around not attacking the door once more:
"Are you calm again? Thank goodness. You mustn't let the hunt overcome you.
Remember yourself. You are not a beast."

If you ignore Iosefka's pleading and attack the door again:
"You are no more than a beast. I should've known…."

Sources

Iosefka's Blood Vial
Blood vial acquired from the lady doctor at Iosefka's clinic.
This refined blood, highly invigorating, restores a larger
amount of HP.
This rare blood vial is a product of a slow and careful
refinement process, likely devised by the doctor herself.

White Church Hat
Attire of special Church doctors.
These doctors are superiors to the black preventative
hunters, and specialists in experimentally backed blood
ministration and the scourge of the beast.
They believe that medicine is not a means of treatment but
rather a method for research, and that some knowledge can
only be obtained by exposing oneself to sickness.

Surgical Long Gloves
White surgical gloves. The intricate embroidery weaves a
spell that protects the wearer.
The Church engages in the hunt in a medical capacity.
When a cancer is discovered, one must pinpoint its location,
reach in, and wrench it from the host's bosom.

Communion Rune
A secret symbol left by Caryll, runesmith of Byrgenwerth.
Several runes relate to "Blood," including "Communion,"
which raises the maximum number of blood vials
one may carry.
The rune represents the Healing Church and its
ministers. Blood ministration is, of course, the pursuit
of communion.

Blood Vial
Special blood used in ministration. Restores HP.
Once a patient has had their blood ministered, a unique but
common treatment in Yharnam, successive infusions recall
the first, and are all the more invigorating for it.
No surprise that most Yharnamites are heavy users of blood.

Sedative
Liquid medicine concoted at Byrgenwerth.
Calms the nerves.
Those who delve into the arcane fall all-too-easily to
madness, and thick human blood serves to calm the frayed
nerves of these inquisitive minds. Naturally, this often leads
to a reliance on blood ministration.

Sullied Bandage
Bandage worn upon awakening to the nightmare of blood
and beasts. Terribly worn and unsanitary.
A faint memory recalls blood ministration, involving the
transfusion of unknown blood.
Not long after, the nightmare began.

Blood Minister dialogue:
Oh yes… Paleblood. Heh. Well you've come to the right place.
Yharnam is the home of blood ministration, you need only unravel its mystery. But where's an outsider like yourself to begin? Easy, with a bit of Yharnam blood of your own.
But first… you need a contract.
Good, all signed and sealed. Now let's begin the transfusion. Oh don't you worry, whatever happens you may think it all a mere bad dream.

Gilbert dialogue:
“The church controls all knowledge on blood ministration, and all varieties of blood.”